1. Field of the Invention
The present invention relates to a balanced high-frequency mixer formed around a circuit of the "Balun" type mainly constituted by a dielectric substrate supporting configurations of conductor material such as lines and ground plane situated in parallel or coinciding planes.
2. Description of the Related Art
Generally, the balanced high-frequency mixers using circuits of the microstrip type are constituted by a coupler having a strong coupling (3 dB) associated to diodes combining the non-linear element of the mixer. Such a coupler is presented in European Patent Application No. 0 213 864 describing a circuit of the "Balun" type, that is to say, a circuit allowing to couple a balanced line with a non-balanced line. In said Patent Application the "Balun" circuit is thus mainly constituted by a dielectric substrate on whose surface lines of conductor material are deposited. It is a well known fact that when the substrate presents a considerable dielectric loss, the operation of the mixer will be degraded. Thus, the conventional solution consists of producing a mixer manufactured on a low-loss substrate also called noble substrate, such as teflon glass, duroid or as it is proposed in above Patent Application, a ceramic or a semiconductor material. The main disadvantage of the choice of this type of substrate relates to the manufacturing cost of the mixer.